The present invention relates to a device which within a radio frequency band, selects from among a number of radio signals one radio signal which is marked in a special way, e.g. in the form of a low-frequency tone modulationg the carrier. The device includes known receiving equipment comprising a high-frequency unit for the reception of the radio signals, a local oscillator and connected thereto a time base circuit which when activated, controls the local oscillator by its output scanning voltage. The local oscillator is actuated by the mentioned output scanning voltage so that it will vary its output frequency within a predetermined frequency range. Furthermore, the receiving equipment comprises a mixer stage connected to the outputs of the high-frequency unit and the local oscillator; and intermediate-frequency stage connected to and following the mixer stage, the intermediate-frequency stage producing an amplified signal each time the varying output frequency from the local oscillator corresponds, in a prescribed way, to a radio signal; a discriminator connected to and following the intermediate-frequency stage and an identification circuit arranged to be activated during the sensing periods of the radio signals respectively and responsive to the mentioned special marking. The discriminator, in this connection, is of that type which on its first output gives a signal equivalent to the marking modulated on the carrier, and on a second output gives the so called discriminating signal which indicates the occurrence of the carrier. The discriminating signal is henceforth also called control signal.